Vacuum plasma generators are known in various power classes and with various output signal forms.
In vacuum glass coating, for example, medium frequency (MF) generators having an MF output signal with powers between 30 and 300 kW are used. The MF signal is mostly a sinusoidal signal with frequencies between 10 kHz and 200 kHz. The output voltages may be from several 100 V to over 1000 V. In order to ignite the plasma, the voltages are often very much higher than during normal operation.
In the plasma, brief and also longer-lasting flashovers may occur, so-called arcs, which are undesirable. An arc is generally identified by means of a collapse or decrease of the voltage and an increase of the current, in particular at the output of the generator or at another location in the generator. If such an arc is identified, it must be ensured that it is extinguished as quickly as possible or does not develop completely.
EP 1 720 195 A1 discloses an arc extinction arrangement in a gas discharging device which is operated with alternating current voltage, in particular MF alternating current voltage, having an arc extinguishing device and an arc identification device which controls it, the arc extinction device having at least one controllable resistor which is arranged in series connection in an electrical line which extends from an alternating current voltage source to an electrode of the gas discharging device. As a controllable resistor, a switch, in particular an IGBT, is provided. When an arc is identified, the switches are switched into a conductive state in such a manner that electrical energy is deliberately converted into heat therein. The depletion layer is greatly heated in the IGBT so that only a few arcs can consequently be processed without leading to destruction of the IGBT.